Sunan Abi Dawud Book 2, Hadith 48
'Abd Allah b. Rabah al-Ansari, whom the Ansar called faqih (juries), came to us from Medina, and reported us on the authority of Abu Qatadah al-Ansari, the horseman of the Messenger of Allah (ﷺ) saying: The Messenger of Allah (ﷺ) sent a military expedition consisting of the chief Companions. He then narrated the same story, saying Nothing awakened us except the rising sun. We stoop up in bewilderment, for our prayer. The Prophet (ﷺ) said: Wait a little, wait a little. When the sun rose high, the Messenger of Allah (ﷺ) said: Those who sued to observer the two rak'ahs of Fajr prayer (sunnah prayer before obligatory prayer) should observe them. Then those who used to observe and those who would not observe stood up and said prayer. Then the Messenger of Allah (ﷺ) commanded to call for prayer; the call for prayer was made accordingly. The Messenger of Allah (ﷺ) stood and led us in prayer. When he turned away (from the prayer) he said: We thank Allah for the fact that we were not engaged in any wordily affairs which detained us from our prayer. Instead our souls were in the hands of Allah. He released them whenever He wished. If any one of you gets morning prayer tomorrow at its proper time, he should offer a similar prayer as an atonement.
"The Prophet (ﷺ) was on a journey. The Prophet (ﷺ) took a turn and I also took a turn with him. He said: 'Look!' I said: 'This is a rider; these are two riders; and these are three' until we became seven. He then said: Guard for us our prayer, i.e. the Fajr prayer. But sleep dominated them and none could awaken them except the heat of the sun. They stood up and drove away a little. Then they got down (from their mounts) and performed ablution. Bilal called for prayer and they offered two rak'ahs of (Sunnah) of Fajr and then offered the Fajr prayer and mounted (their mounts). Some of them said to others: We showed negligence in prayer. The Prophet (ﷺ) said: There is no negligence in sleep. The negligence is in wakefulness. If any of you forget saying prayer, he should offer it when he remembers it and next day (he should say it) at its proper time.
"Allah takes your souls as He wishes, and returns them as He wishes. Stand up and call the Adhan to prayer." They (the Companions) stood and performed ablution. When the sun rose high, the Prophet (ﷺ) stood and led the people in prayer.